Vertical transistor device comprising a two-dimensional (2D) material positioned in a channel region of the device and methods of making such vertical transistor devices

ABSTRACT

One illustrative vertical transistor device disclosed herein includes a channel region comprising at least one layer of a two-dimensional (2D) material, a bottom source/drain region, a top source/drain region and a gate structure positioned all around at least the at least one layer of a two-dimensional (2D) material.

BACKGROUND Field of the Invention

The present disclosure generally relates to various novel embodiments of a vertical transistor device comprising at least one layer of a two-dimensional (2D) material positioned in a channel region of the device and methods of making such vertical transistor devices.

Description of the Related Art

Within the electronics industry, there is a constant demand for reducing the size of semiconductor devices while at the same time improving their performance capabilities. Relatively recently, materials that are generally known as two-dimensional (2D) materials have been developed and investigated for use in integrated circuit products. In general, a 2D material is a material having a single-layer structure in which atoms form a predetermined crystal structure. The atoms or molecules within such a single layer of 2D material are bonded together through intermolecular forces (e.g., covalent bonds). Adjacent layers of 2D materials of a stacked structure are coupled to one another through one or more intermolecular forces (e.g., Van der Waals forces). Many of the intrinsic electronic, thermal, optical and mechanical properties of such 2D materials, such as graphene, exceed, in isolation or combination, that of other materials commonly used in the manufacture of integrated circuit products and various semiconductor devices, such as transistors. For example, depending on their chemical structure, single-sheet 2D materials may possess many beneficial properties, such as high mechanical strength, high electronic and thermal conductivity, and/or unique quantum-mechanical effects, etc.

In modern integrated circuits, such as microprocessors, storage devices and the like, a very large number of circuit elements, especially transistors, are provided on a restricted chip area. Transistors come in a variety of shapes and forms, e.g., planar transistors, FinFET transistors, nanowire devices, vertical transistors, etc. The transistors are typically either NMOS (NFET) or PMOS (PFET) type devices wherein the “N” and “P” designation is based upon the type of dopants used to create the source/drain regions of the devices. CMOS (Complementary Metal Oxide Semiconductor) technology or products refers to integrated circuit products that are manufactured using both NMOS and PMOS transistor devices. Irrespective of the physical configuration of the transistor device, each device comprises drain and source regions and a gate electrode structure positioned between the source/drain regions. Upon application of an appropriate control voltage to the gate electrode, a conductive channel region forms between the drain region and the source region.

In general, prior art vertical transistor devices comprise a generally vertically oriented channel semiconductor structure that extends upward from a front surface of a semiconductor substrate. Such a vertical transistor device further comprises a channel region, a gate-all-around (GAA) gate structure that is positioned around the perimeter of the channel region in the vertically oriented channel semiconductor structure, a bottom source/drain (S/D) region, a top S/D region, a bottom spacer, and a top spacer. A bottom source/drain contact is formed to conductively contact the bottom S/D region, a top source/drain contact is formed to conductively contact the top S/D region and a gate contact is formed to conductively contact the gate structure. The gate structure typically comprises a gate insulation layer and a conductive gate electrode. The gate structure may be manufactured using well-known gate first or replacement gate manufacturing techniques.

The present disclosure is generally directed to various novel embodiments of a vertical transistor device comprising at least one layer of a two-dimensional (2D) material positioned in a channel region of the device and methods of making such vertical transistor devices.

SUMMARY

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

Generally, the present disclosure is directed to various novel embodiments of a vertical transistor device comprising at least one layer of a two-dimensional (2D) material positioned in a channel region of the device and methods of making such vertical transistor devices. One illustrative vertical transistor device disclosed herein includes a channel region comprising at least one layer of a two-dimensional (2D) material, a bottom source/drain region, a top source/drain region and a gate structure positioned all around at least the at least one layer of a two-dimensional (2D) material.

Another illustrative vertical transistor device disclosed herein includes a bottom source/drain region, a top source/drain region and a channel region comprising a plurality of individual layers of 2D material positioned in a vertically stacked arrangement between the bottom source/drain region and the top source/drain region. In this example, each of the plurality of layers of 2D material have a periodic crystallographic pattern and, relative to a reference axis of rotation, the periodic crystallographic pattern of one of the plurality of layers of 2D material is rotated relative to the periodic crystallographic pattern of another of the plurality of layers of 2D material. The device also includes a gate structure positioned all around at least a portion of the plurality of individual layers of 2D material.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

FIGS. 1-20 depict various novel embodiments of a vertical transistor device comprising at least one layer of a two-dimensional (2D) material positioned in a channel region of the device and methods of making such vertical transistor devices.

While the subject matter disclosed herein is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

Various illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

The present subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present disclosure with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.

As will be readily apparent to those skilled in the art upon a complete reading of the present application, the presently disclosed method may be applicable to a variety of products, including, but not limited to, logic products, memory products, etc. With reference to the attached figures, various illustrative embodiments of the methods and devices disclosed herein will now be described in more detail.

FIGS. 1-20 depict various novel embodiments of a vertical transistor device 100 comprising at least one layer of a two-dimensional (2D) material positioned in a channel region of the device and methods of making such vertical transistor devices. As will be appreciated by those skilled in the art after a complete reading of the present application, the vertical transistor device 100 disclosed herein may be an N-type or P-type device and it may be formed on a bulk semiconductor substrate or a semiconductor-on-insulator substrate. Additionally, the gate structure of the vertical transistor device 100 may be manufactured using known gate-first or replacement gate manufacturing techniques. For purposes of disclosure only, the gate structure of the vertical transistor device 100 is formed by performing known replacement gate manufacturing techniques. However, as noted above, the various inventions disclosed herein should not be considered to be limited to the particular examples shown in the attached drawings and described below.

FIG. 1 depicts one illustrative embodiment of a vertical transistor device 100 disclosed at an early stage of fabrication. As shown therein, a first semiconductor substrate 102 with a plurality of 2D material layers 104A-104B formed above a surface 102S thereof is positioned opposite a second semiconductor substrate 103 with a plurality of 2D material layers 104C-104D formed above a surface 103S thereof. The 2D material layers 104A-104D will be collectively referenced using the numeral 104. The number of the 2D material layers 104 formed on each of the substrates 102, 103 may vary depending upon the particular application, and the number of 2D material layers 104 formed on each of the substrates 102, 103 need not be the same, but that may be the case in some applications. In other applications, only a single 2D material layer 104 may be formed on one of the substrates 102, 103 while the other of the substrates 102, 103 has a plurality of 2D material layers 104 formed thereon, e.g., the substrate 102 may have a single 2D material layer 104 formed thereon while the substrate 103 may have five 2D material layers 104 formed thereon. In another embodiment, all of the 2D material layers 104 may be formed on one of the substrates 102, 103, while the other of the substrates 102, 103 may have no 2D material layers 104 formed thereon. In this latter case, the substrate without any 2D material layers 104 would be bonded to the uppermost 2D material layer 104 formed on the other substrate.

The substrates 102, 103 may have a bulk configuration (as depicted in FIG. 1) or a semiconductor-on-insulator or silicon-on-insulator (SOI) configuration (not shown) that includes a base semiconductor layer, a buried insulation layer (e.g., silicon dioxide), and an active layer (e.g., silicon), wherein semiconductor devices are formed in and above the active layer. The substrates 102, 103 may be made of silicon or they may be made of semiconductor materials other than silicon and they may be formed to any desired thickness. Additionally, the substrates 102, 103 need not be made of the same material or have the same thickness, but that may the case in some applications. Thus, the terms “substrate” or “semiconductor substrate” should be understood to cover all semiconducting materials and all forms of such semiconductor materials.

As will be appreciated by those skilled in the art after a complete reading of the present application, the 2D material layers 104 disclosed herein may be formed using any known technique for the formation of such 2D material layers 104. For example, the 2D material layers 104 disclosed herein (or vertical stacks of such layers) may be formed using the methods disclosed in US patent applications 20190070840, 20180093454 or 20180205038, the entirety of each of these patent applications is hereby incorporated by reference. Additionally, the 2D material layers 104 disclosed herein (or vertical stacks of such layers) may be produced by layer formation and cleaving techniques that are similar to known techniques for forming SOI substrates which are also incorporated herein. Each of the 2D material layers 104 disclosed herein is a material having a single-layer structure in which the atoms or molecules of the layer 104 form a predetermined crystalline structure. The 2D material layers 104 disclosed herein may comprise a variety of materials, e.g., silicon, silicon germanium, a metal chalcogenide based material, a transition metal dichalcogenide (TMD), graphene, MoS₂, MoSe₂, MoTe₂, WS₂, WSe₂, WTe₂, HfS₂, HfSe₂, ZrS₂, ZrSe₂, NbSe₂, ReSe₂, etc.

In some embodiments, as described more fully below, the 2D material layers 104 disclosed herein may be formed such that the crystalline structure of adjacent layers of the 2D material layers 104 may be rotated (clockwise or counterclockwise) relative to one another. Such rotated 2D material layers 104 may be formed using any technique known in the art, including, for example, the method disclosed in the above-referenced US patent application 20180205038. The thickness of each of the 2D material layers 104 disclosed herein may vary depending upon the particular application, e.g., 1-100 nm. In the case where multiple 2D material layers 104 are arranged in a vertically oriented stack, the thickness and/or material of composition for each of the 2D material layers 104 within the stack may be different from one another. In some applications, all of the 2D material layers 104 in a particular stack of such layers may all have the same approximate thickness and they all may be comprised of the same material, but that may not be the case in all applications. If desired, during the process of forming the 2D material layers 104, N- or P-type dopant materials may be added to each of the 2D material layers 104. In some applications, all of the 2D material layers 104 in a particular stack of such layers may be doped with the same type of dopant (e.g., N or P) but that may not be the case in all applications. Of course, if desired, and depending upon the particular application, some or all of the 2D material layers 104 disclosed herein may be formed in a substantially un-doped condition and dopant material may be subsequently implanted into the 2D material layers 104 disclosed herein. In other applications, some or all of the 2D material layers 104 disclosed herein may be initially formed in a substantially un-doped condition and remain substantially un-doped in the final vertical transistor device 100.

In one illustrative process flow, the 2D material layers 104 disclosed herein are continuous layers of material that have a three dimensional configuration, i.e., a width in the direction W and length (into and out of the plane of the drawing page) and a substantially uniform vertical thickness in a direction that is substantially normal to the surfaces 102S, 103S of the substrates 102, 103, respectively, across the entire length and width of the 2D material layer 104. In one illustrative embodiment, each of the 2D material layers 104 disclosed herein are continuous sheets of material(s) that have a substantially planar surface 104U and a substantially planar surface 104R. The substantially planar surface 104U and the substantially planar surface 104R of each of the 2D material layers are substantially parallel to one another and both of these surfaces are substantially continuous across the entire length and width of the 2D material layer 104 at this point in the process flow.

FIG. 2 depicts the vertical transistor device 100 after the substrates 102, 103 have been bonded to one another using known manufacturing techniques. More specifically, the 2D material layer 104B on the substrate 102 was bonded to the 2D material layer 104C on the substrate 103. In other applications, the features may be encapsulated with deposited layers of material if the Van der Waals bonding does not provide sufficient mechanical strength.

FIG. 3 depicts the vertical transistor device 100 after a patterned etch mask 108 was formed above the substrate 103. In one illustrative example, the patterned etch mask 108 may be a patterned layer of photoresist or OPL. In other applications, the patterned etch mask 108 may be a patterned hard mask that is comprised of, for example, silicon nitride. Such a patterned hard mask may be formed by performing known deposition, masking and etching techniques.

FIG. 4 depicts the vertical transistor device 100 after one or more etching processes were performed through the patterned etch mask 108 so as to define a plurality of trenches 105 in the substrate 102. This etching process also patterns the 2D material layers 104 so as to define a channel region 120 for the vertical transistor device 100. The etching process also patterns the substrate 103 into a patterned upper substrate portion 103P positioned above the channel region 120. The etching process also patterns the substrate 102 into a patterned lower substrate portion 102P positioned below the channel region 120. As will be appreciated by those skilled in the art after a complete reading of the present application, the patterned upper substrate portion 103P will eventually be doped and function as the upper or top source/drain region of the vertical transistor device 100, while the patterned lower substrate portion 102P will ultimately be doped and function as the lower or bottom source/drain region for the vertical transistor device 100. At this point in the process flow, as indicated in the right-hand portion of FIG. 4, the patterned upper substrate portion 103P, the channel region 120 (i.e., the patterned 2D material layers 104) and the patterned lower substrate portion 102P (all of the regions 103P, 120 and 102P being collectively referenced with the numeral 122) may have a variety of different configurations when viewed from above, e.g., circular, rectangular, square, etc., and each of the regions 103P, 120 and 102P has an outer perimeter 122P.

FIG. 5 depicts the vertical transistor device 100 after a simplistically depicted sidewall spacer 106 was formed adjacent the patterned upper substrate portion 103P, the channel region 120 and the patterned lower substrate portion 102P. The sidewall spacer 106 was formed by depositing a layer of spacer material and thereafter performing an anisotropic etching process on the layer of spacer material. The sidewall spacer 106 may be formed to any desired thickness (as measured at its base) and it may be comprised of any desired material, e.g., silicon nitride, a low-k insulating material (k value of 7 or less), silicon dioxide, etc.

FIG. 6 depicts the vertical transistor device 100 after several process operations were performed. First, a patterned implant mask (not shown) was formed on the product. Thereafter, one or more angled ion implantation processes 107 were performed to form a bottom source/drain (S/D) region 109 for the vertical transistor device 100 in the patterned lower substrate portion 102P as well as the other portions of the substrate 102. The bottom source/drain (S/D) region 109 may be doped with an appropriate dopant (e.g., N-type or P-type) depending upon the type of vertical transistor device 100 (N or P) under construction. The patterned upper substrate portion 103P may or may not be masked during this implant process operation. Thereafter, the patterned implant mask was removed.

FIG. 7 depicts the vertical transistor device 100 after a layer of insulating material 110 was formed on the product and after its upper surface 110X was planarized by performing a chemical mechanical planarization (CMP) process. The layer of insulating material 110 may be comprised of a variety of different materials, e.g., silicon nitride, a low-k insulating material (k value of 7 or less), silicon dioxide, etc.

FIG. 8 depicts the vertical transistor device 100 after a timed recess etching process was performed to recess the layer of insulating material 110 and the sidewall spacer 106 to a desired residual vertical thickness, thereby forming a bottom spacer 111 that is comprised of the layer of insulating material 110 and the sidewall spacer 106. After this etching process, the layer of insulating material 110 and the sidewall spacer 106 have recessed upper surfaces 110R, 106R, respectively.

In the illustrative example depicted herein, the gate structure for the vertical transistor device 100 will be formed by performing well-known gate-first manufacturing techniques. However, as will be appreciated by those skilled in the art after a complete reading of the present application, the gate structure for the vertical transistor device 100 disclosed herein may also be formed by performing well-known replacement gate manufacturing techniques. Accordingly, FIG. 9 depicts the vertical transistor device 100 after representative gate structure materials 112 have been formed on the product. The gate structure materials 112 normally comprise a conformal gate insulation layer 112A, such as silicon dioxide or a high-k (k value greater than 10) insulating material, and one or more layers of conductive material 112B that act as the gate electrode, e.g., a metal, a metal alloy, titanium nitride, tantalum nitride, tungsten, aluminum, polysilicon, etc.

FIG. 10 depicts the vertical transistor device 100 after one or more timed recess etching processes were performed to recess the conformal gate insulation layer 112A and the one or more layers of conductive material 112B to a desired residual vertical thickness. After this process is completed, the one or more layers of conductive material 112B have a recessed upper surface 112R.

FIG. 11 depicts the vertical transistor device 100 after several process operations were performed. First a patterned etch mask (not shown)—generally known as a gate cut mask—was formed so as to permit patterning the materials 112B, 112A so as to thereby define the final gate structure for the vertical transistor device 100. The T patterned etch mask may be made of any desired material, e.g., OPL, and it may be formed using traditional techniques. Thereafter, one or more anisotropic etching processes were performed through the patterned etch mask to remove the exposed portions of the materials 112B, 112A so as to form the final gate structure 112G. Thereafter, the patterned etch mask was removed. It should be noted that the 2D material layers 104 need not, but may, cover the entire axial length of the channel region of the completed device in the gate length direction (i.e., vertical as indicated by GL in FIG. 11) of the vertical transistor device 100. That is, the final gate structure 112G for the vertical transistor device 100 may have a length in the gate length direction (GL) of the vertical transistor device 100 that is greater than, less than or substantially equal to the combined vertical thickness of all of the 2D material layers 104 formed for the vertical transistor device 100.

FIG. 12 depicts the vertical transistor device 100 after several process operations were performed. First, a patterned implant mask (not shown) was formed on the product. Thereafter, one or more angled ion implantation processes 114 was performed to form a top or upper source/drain (S/D) region 115 for the vertical transistor device 100 in the patterned upper substrate portion 103P. The top source/drain (S/D) region 115 may be doped with an appropriate dopant (e.g., N-type or P-type) depending upon the type of vertical transistor device 100 (N or P) under construction. Typically, the top source/drain (S/D) region 115 will be doped substantially the same as the bottom source/drain region 109 described above. Thereafter, the patterned implant mask was removed.

FIG. 13 depicts the vertical transistor device 100 after several process operations were performed. First a layer of insulating material 116 was formed on the product. Next, the upper surface of the layer of insulating material 116 was planarized by performing a CMP process. Thereafter, a timed recess etching process was performed to recess the layer of insulating material 116 a desired residual vertical thickness, thereby forming a top spacer for the vertical transistor device 100. The layer of insulating material 116 may be comprised of a variety of different materials, e.g., silicon nitride, a low-k insulating material (k value of 7 or less), silicon dioxide, etc.

FIG. 14 depicts the vertical transistor device 100 after several process operations were performed. First, a representative one or more layers of insulating material 117 were formed above the layer of insulating material 116. As will be appreciated by those skilled in the art, the one or more layers of insulating material 117 is intended to be representative of any of a variety of combinations or insulating materials and etch stop layers. The one or more layers of insulating material 117 may comprise a variety of different materials, e.g., silicon dioxide, a low-k material, silicon nitride, etc. and these layers of material may be formed to any desired thickness. Next, known manufacturing techniques were performed to form a bottom source/drain contact structure 118A, a top source/drain contact structure 118B and a gate contact structure 118C (collectively referenced using the numeral 118) in the one or more layers of insulating material 117. The contact structures 118 are intended to be schematic and representative in nature, as they may be formed using any of a variety of different conductive materials and by performing traditional manufacturing operations. The contact structures 118 may also contain one or more barrier layers (not depicted). In one illustrative example, the contact structures 118 may be formed by forming contact openings in the various insulating material layers 117 to expose the desired landing point for the contact, and thereafter depositing a liner, e.g., Ti, TiN, in the contact openings. Then, a deposition process may be performed so as to overfill the contact openings with a conductive material, such as tungsten or cobalt. Thereafter, a CMP process may be performed to planarize the upper surface of the layer of insulating material 117, which results in the removal of excess portions of the liner and the tungsten (or cobalt) positioned above the layer of insulating material 117 outside of the contact openings and the formation of the contact structures 118.

With continuing reference to FIG. 14, note that the lowermost surface of the lowermost layer of 2D material 104A is positioned on and in contact with the bottom source/drain region 109, while the uppermost surface of the uppermost layer of 2D material 104D is positioned on and in contact with the top source/drain region 115. Also note that, in the example depicted herein, the gate structure 112G has a dimension in the gate length direction (GL) of the vertical transistor device 100 that is substantially equal to the combined vertical thickness of all of the plurality of individual layers of 2D material 104A-D.

As described above, the 2D material layers 104 disclosed herein have a periodic crystallographic pattern. In one illustrative embodiment, where the various embodiments of the vertical transistor device 100 disclosed herein comprise at least two of the 2D material layers 104, the periodic crystallographic pattern of vertically adjacent 2D material layers 104 may be rotated or “twisted” relative to one another so as to improve the electrical performance of the combination of the at least two layers of the 2D material 104, such as, for example, charge carrier mobility, gate control, gate capacitance, short channel effects, etc. The amount of or degree of relative rotation between the 2D material layers 104 may be determined with respect to any axis of rotation. For example, such a reference axis of rotation may be a line that is substantially normal to the upper surface 102S of the substrate 102. Other reference axes are, or course, possible. Moreover, the direction of relative rotation between the 2D material layers 104 (clockwise or counterclockwise) may vary as well. Of course, depending upon the material selected for the 2D material layers 104, e.g., graphene or MoS₂, the periodic crystallographic pattern of the 2D material layers may be different. In FIGS. 15-20, each of the 2D material layers 104 is depicted as being comprised of silicon.

FIG. 15 is a top view of a single layer of 2D material 104 disclosed herein showing the periodic crystallographic pattern of each of the 2D material layers 104.

FIG. 16 is a plan view of two of the 2D material layers 104 in a stacked arrangement wherein the uppermost of the two 2D material layers 104 is rotated about 8° in a clockwise direction relative to the bottom layer of the two 2D material layers 104.

FIG. 17 is a plan view of three of the 2D material layers 104 in a stacked arrangement wherein the second of the three 2D material layers 104 is rotated about 8° in a clockwise direction relative to the bottom layer of the three 2D material layers 104 and the uppermost of the three 2D material layers 104 is rotated about 8° in a clockwise direction relative to the second layer of the three 2D material layers 104. Thus, in relative terms, the uppermost of the three 2D material layers 104 is rotated in a clockwise direction about 16° relative to the bottom layer of the three 2D material layers 104.

FIG. 18 is a plan view of two of the 2D material layers 104 in a stacked arrangement wherein the uppermost of the two 2D material layers 104 is rotated about 12° in a clockwise direction relative to the bottom layer of the two 2D material layers 104.

FIG. 19 is a plan view of three of the 2D material layers 104 in a stacked arrangement wherein the second of the three 2D material layers 104 is rotated about 12° in a clockwise direction relative to the bottom layer of the three 2D material layers 104 and the uppermost of the three 2D material layers 104 is rotated about 12° in a clockwise direction relative to the second layer of the three 2D material layers 104. Thus, in relative terms, the uppermost of the three 2D material layers 104 is rotated in a clockwise direction about 24° relative to the bottom layer of the three 2D material layers 104.

FIG. 20 is a plan view of a stack of the 2D material layers 104 that is similar to that shown in FIG. 17 except that a fourth 2D material layer has been positioned above the uppermost of the three of the 2D material layers 104 shown in FIG. 17, and the fourth layer of 2D material shown in FIG. 20 has been rotated about 8° in a clockwise direction relative to the third layer of the four 2D material layers 104 shown in FIG. 20. Thus, in relative terms, the uppermost of the four 2D material layers 104 shown in FIG. 20 is rotated in a clockwise direction about 24° relative to the bottom layer of the four 2D material layers 104 shown in FIG. 20.

Of course, as will be appreciated by those skilled in the art after a complete reading of the present application, the relative rotation between the 2D material layers 104 need not be constant for all of the 2D material layers 104 in a given stack of such materials. For example, the second layer of a four layer stack of materials may be rotated 7° relative to the bottom layer, the third layer of the stack may be rotated 15° relative to the second layer of the stack of materials, and the fourth layer of the stack may be rotated 6° relative to the third layer of the stack of such materials. Additionally, the direction of relative rotation may be different for various layers in the stack of such three 2D material layers. Moreover, in some cases, the direction of relative rotation among all of the 2D material layers within a given stack of such may be the same, but that may not be the case in all applications.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, the process steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is there-fore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Note that the use of terms, such as “first,” “second,” “third” or “fourth” to describe various processes or structures in this specification and in the attached claims is only used as a shorthand reference to such steps/structures and does not necessarily imply that such steps/structures are performed/formed in that ordered sequence. Of course, depending upon the exact claim language, an ordered sequence of such processes may or may not be required. Accordingly, the protection sought herein is as set forth in the claims below. 

The invention claimed is:
 1. A vertical transistor device, comprising: a channel region comprising at least one layer of a two-dimensional (2D) material; a bottom source/drain region; a top source/drain region, wherein the at least one layer of 2D material comprises a plurality of individual layers of 2D material positioned in a vertically stacked arrangement between the bottom source/drain region and the top source/drain region, each of the plurality of layers of 2D material having a periodic crystallographic pattern that is rotated relative to a periodic crystallographic pattern of another of the plurality of layers of 2D material; and a gate structure positioned all around at least one layer of the plurality of layers of two-dimensional (2D) material.
 2. The vertical transistor device of claim 1, wherein the at least one layer of 2D material has a substantially planar upper surface, a substantially planar bottom surface and a substantially uniform vertical thickness across an entire length of the at least one layer of 2D material in a gate length direction of the vertical transistor device.
 3. The vertical transistor device of claim 1, wherein a lowermost surface of the at least one layer of 2D material is positioned on and in contact with the bottom source/drain region and an uppermost surface of the at least one layer of 2D material is positioned on and in contact with the top source/drain region.
 4. The vertical transistor device of claim 1, wherein the bottom source/drain region comprises a doped first semiconductor material and the top source/drain region comprises a doped second semiconductor material, wherein the first semiconductor material and the second semiconductor material comprise a same semiconductor material.
 5. The vertical transistor device of claim 1, wherein each of the plurality of layers of 2D material comprise a same 2D material.
 6. The vertical transistor device of claim 1, wherein each of the plurality of layers of 2D material have a vertical thickness that is substantially the same.
 7. The vertical transistor device of claim 1, wherein the at least one layer of 2D material comprises one of silicon, silicon germanium, a metal chalcogenide based material, a transition metal dichalcogenide (TMD), graphene, MoS₂, MoSe₂, MoTe₂, WS₂, WSe₂, WTe₂, HfS₂, HfSe₂, ZrS₂, ZrSe₂, NbSe₂, or ReSe₂.
 8. The vertical transistor device of claim 1, wherein the gate structure has a dimension in a gate length direction of the vertical transistor device that is substantially equal to a combined vertical thickness of the plurality of individual layers of 2D material.
 9. The vertical transistor device of claim 1, wherein the top source/drain region is positioned on and in contact with an uppermost layer of the plurality of layers of 2D material and a lowermost layer of the plurality of layers of 2D material is positioned on and in contact with the bottom source/drain region.
 10. A vertical transistor device, comprising: a bottom source/drain region; a top source/drain region; a channel region comprising a plurality of individual layers of 2D material positioned in a vertically stacked arrangement between the bottom source/drain region and the top source/drain region, wherein each of the plurality of layers of 2D material have a periodic crystallographic pattern and wherein, relative to a reference axis of rotation, the periodic crystallographic pattern of one of the plurality of layers of 2D material is rotated relative to the periodic crystallographic pattern of another of the plurality of layers of 2D material; and a gate structure positioned all around at least a portion of the plurality of individual layers of 2D material.
 11. The vertical transistor device of claim 10, wherein each of the plurality of individual layers of 2D material has a substantially planar upper surface, a substantially planar bottom surface and a substantially uniform vertical thickness across an entire length of the plurality of individual layers of 2D material in a gate length direction of the vertical transistor device.
 12. The vertical transistor device of claim 11, wherein the bottom source/drain region comprises a doped first semiconductor material and the top source/drain region comprises a doped second semiconductor material, wherein the first semiconductor material and the second semiconductor material comprise a same semiconductor material.
 13. The vertical transistor device of claim 11, wherein each of the plurality of layers of 2D material comprises a same 2D material and wherein each of the plurality of layers of 2D material has a vertical thickness in a gate length direction of the vertical transistor device that is substantially the same.
 14. The vertical transistor device of claim 11, wherein the gate structure has a dimension in a gate length direction of the vertical transistor device that is substantially equal to a combined vertical thickness of the plurality of individual layers of 2D material.
 15. The vertical transistor device of claim 11, wherein the top source/drain region is positioned on and in contact with an uppermost layer of the plurality of layers of 2D material and the lowermost layer of the plurality of layers of 2D material is positioned on and in contact with the bottom source/drain region.
 16. A vertical transistor device, comprising: a bottom source/drain region comprising a doped first semiconductor material; a top source/drain region comprising a doped second semiconductor material, wherein the first semiconductor material and the second semiconductor material comprise a same semiconductor material; a channel region comprising a plurality of individual layers of 2D material positioned in a vertically stacked arrangement between the bottom source/drain region and the top source/drain region, wherein each of the plurality of layers of 2D material have a periodic crystallographic pattern and wherein, relative to a reference axis of rotation, the periodic crystallographic pattern of one of the plurality of layers of 2D material is rotated relative to the periodic crystallographic pattern of another of the plurality of layers of 2D material, wherein the top source/drain region is positioned on and in contact with an uppermost layer of the plurality of layers of 2D material and the lowermost layer of the plurality of layers of 2D material is positioned on and in contact with the bottom source/drain region; and a gate structure positioned all around at least a portion of the plurality of individual layers of 2D material.
 17. The vertical transistor device of claim 16, wherein each of the plurality of individual layers of 2D material has a substantially planar upper surface, a substantially planar bottom surface and a substantially uniform vertical thickness across an entire length of the plurality of individual layers of 2D material in a gate length direction of the vertical transistor device.
 18. The vertical transistor device of claim 16, wherein the gate structure has a dimension in a gate length direction of the vertical transistor device that is substantially equal to a combined vertical thickness of the plurality of individual layers of 2D material. 